1. Field of the Invention
The present invention relates to the field of data communications networks. More particularly, the present invention relates to an apparatus and method for automatic network device cluster discovery.
2. Background
A network is a communication system that links two or more computers and peripheral devices, and allows users to access resources on other computers and exchange messages with other users. A network allows users to share resources on their own systems with other network users and to access information on centrally located systems or systems that are located at remote offices. It may provide connections to the Internet or to the networks of other organizations. The network typically includes a cable that attaches to network interface cards (“NICs”) in each of the devices within the network. Users may interact with network-enabled software applications to make a network request, such as to get a file or print on a network printer. The application may also communicate with the network software, which may then interact with the network hardware to transmit information to other devices attached to the network.
A local area network (“LAN”) is a network that is located in a relatively small physical area, such as a building, in which computers and other network devices are linked, usually via a wiring-based cabling scheme. A LAN typically includes a shared medium to which workstations attach and through which they communicate. LANs often use broadcasting methods for data communication, whereby any device on the LAN can transmit a message that all other devices on the LAN then “listen” to. However, only the device or devices to which the message is addressed actually receive the message. Data is typically packaged into frames for transmission on the LAN.
Currently, the most common LAN media is Ethernet, which traditionally has a maximum bandwidth of 10 Mbps. Traditional Ethernet is a half-duplex technology, in which each Ethernet network device checks the network to determine whether data is being transmitted before it transmits, and defers transmission if the network is in use. In spite of transmission deferral, two or more Ethernet network devices can transmit at the same time, which results in a collision. When a collision occurs, the network devices enter a back-off phase and retransmit later.
As more network devices are added to a LAN, they must wait more often before they can begin transmitting, and collisions are more likely to occur because more network devices are trying to transmit. Today, throughput on traditional Ethernet LANs suffers even more due to increased use of network-intensive programs, such as client-server applications, which cause hosts to transmit more often and for longer periods of time.
FIG. 1 is a block diagram illustrating a network connection between a user 10 and a server 20. FIG. 1 is an example which may be consistent with any type of network, including a LAN, a wide area network (“WAN”), or a combination of networks, such as the Internet.
When a user 10 connects to a particular destination, such as a requested web page on a server 20, the connection from the user 10 to the server 20 is typically routed through several routers 12A-12D. Routers are internetworking devices. They are typically used to connect similar and heterogeneous network segments into Internetworks. For example, two LANs may be connected across a dial-up line, across the Integrated Services Digital Network (“ISDN”), or across a leased line via routers. Routers may also be found throughout the Internet. End users may connect to a local Internet Service Provider (“ISP”) (not shown).
As the data traffic on a LAN increases, users are affected by longer response times and slower data transfers, because all users attached to the same LAN segment compete for a share of the available bandwidth of the LAN segment (e.g., 10 Mbps in the case of traditional Ethernet). Moreover, LANs commonly experience a steady increase in traffic even if the number of users remains constant, due to increased network usage of software applications using the LAN. Eventually, performance drops below an acceptable level and it becomes necessary to separate the LAN into smaller, more lightly loaded segments.
LANs are becoming increasingly congested and overburdened. In addition to an ever-growing population of network users, several factors have combined to stress the capabilities of traditional LANs, including faster computers, faster operating systems, and more network-intensive software applications.
There are two traditional approaches to relieving LAN congestion. The first is to simply install a faster networking technology, such as FDDI, ATM, or Fast Ethernet. However, these approaches are expensive to implement. The other traditional approach is to use bridges and routers to reduce data traffic between networks. This solution is also relatively expensive both in money and configuration time, and is only effective when inter-segment traffic is minimal. When inter-segment traffic is high, some bridges and routers can become a bottleneck due to their limited processing power. They also require extensive setup and manual configuration in order to maintain their performance. In addition, despite large buffers, packet loss is always a possibility.
Switching is a technology that alleviates congestion in Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI) and other similar LANs by reducing traffic and increasing bandwidth. LAN switches are designed to work with existing media infrastructures so that they can be installed with minimal disruption of existing networks.
A Media Access Control (“MAC”) address is the unique hexadecimal serial number assigned to each Ethernet network device to identify it on the network. With Ethernet devices, this address is permanently set at the time of manufacture. Each network device has a unique MAC address, so that it will be able to receive only the frames that were sent to it. If MAC addresses were not unique, there would be no way to distinguish between two stations. Devices on a network monitor network traffic and search for their own MAC address in each frame to determine whether they should decode it or not. Special circumstances exist for broadcasting to every device on the network.
Ethernet uses variable-length frames of data to transmit information from a source to one or more destinations. Every Ethernet frame has two fields defined as the source and destination addresses, which indicate the MAC addresses of the network devices where a frame originated and where it is ultimately destined, respectively. FIG. 2-A illustrates the structure of an Ethernet frame, as defined by the IEEE. As shown in FIG. 2-A, the Ethernet frame 22 includes a Preamble 24, a Start of Frame Delimiter 26, a Destination Address 28, a Source Address 30, a Length of data field 32 (sometimes used as a Protocol Type field), a variable-length Data field 34, a Pad 36, and a Checksum 38. The Preamble 24 is a seven-byte field, with each byte containing the bit pattern 10101010 to allow for clock synchronization between sending and receiving stations (not shown). The Start of Frame Delimiter 26 is a one-byte field containing the bit pattern 10101011 to denote the start of the frame itself. The Destination Address 28 and the Source Address 30 are typically six-byte fields which specify the unique MAC addresses of the receiving and sending stations. Special addresses allow for multicasting to a group of stations and for broadcasting to all stations on the network. The Length of Data field 32 specifies the number of bytes present in the Data field 34, from a minimum of 0 to a maximum of 1500. The Pad field 36 is used to fill out the length of the entire frame 22 to a minimum of 64 bytes when the Data field 34 contains a small number of bytes. Finally, the Checksum field 38 is a 32-bit hash code of the Data field 34, which can used by the receiving station to detect data transmission errors.
In the context of the present invention, the term “switching” refers to a technology in which a network device (known as a switch) connects two or more LAN segments. A switch transmits frames of data from one segment to their destinations on the same or other segments. When a switch begins to operate, it examines the MAC address of the frames that flow through it to build a table of known sources. If the switch determines that the destination of a frame is on the same segment as the source of the frame, it drops, or filters, the frame because there is no need to transmit it. If the switch determines that the destination is on another segment, it transmits the frame onto the destination segment only. Finally, using a technique known as flooding, if the destination segment is unknown, the switch transmits the frame on all segments except the source segment.
Logically, a LAN switch behaves similarly to a bridge, which is a different kind of network device. The primary difference is that switches have higher data throughput than bridges, because their frame forwarding algorithms are typically performed by application-specific integrated circuits (“ASICs”) especially designed for that purpose, as opposed to the more general purpose (and relatively slower) microprocessors typically used in bridges. Like bridges, switches are designed to divide a large, unwieldy local network into smaller segments, insulating each segment from local traffic on other segments, thus increasing aggregate bandwidth while still retaining full connectivity. Switches typically have higher port counts than bridges, allowing several independent data paths through the device. This higher port count also increases the data throughput capabilities of a switch.
Because a switch maintains a table of the source MAC addresses received on every port, it “learns” to which port a station is attached every time the station transmits. Then, each packet that arrives for that station is forwarded only to the correct port, eliminating the waste of bandwidth on the other ports. Since station addresses are checked every time a switch receives a packet from a station, if a station is relocated, the switch will reconfigure its forwarding table immediately upon receiving a transmission from the station.
Referring now to FIG. 2-B, a block diagram of an Ethernet switch according to one aspect of the present invention is shown. As shown in FIG. 2-B, Ethernet switch 200 includes a Layer 1 Physical Interface (“PHY”) 202, 204, and a Layer 2 Media Access Control Interface (“MAC”) 206, 208, for each port on the Ethernet switch 200. A network interface card (“NIC”) consists of a MAC and a PHY. An Ethernet switch also contains a MAC and PHY on every port. Thus, an Ethernet switch may appear to a network as multiple NICs coupled together. Each switch PHY 202, 204, receives the incoming data bit stream and passes it to its corresponding MAC 206, 208, which reassembles the original Ethernet frames.
Ethernet switch 200 also includes a frame buffer memory 210, 212, for each port, a source address table memory 220, discovery protocol logic 230, learning logic 240, forwarding logic 250, packet redirection logic 260, and a configuration and management interface 270. During operation, the learning logic 240 will look at the source address (“SA”) within a received Ethernet frame and populate the Source Address Table (“SAT”) memory 220 with three columns: MAC address 280, port number 282, and age 284. The MAC address is the same as the source address that a sender has embedded into the frame. The age item will be a date stamp to indicate when the last frame was received from a particular MAC SA. In the example shown in FIG. 2-B, the port number may be 1 or 2. The SAT is also known as the Switch Forwarding Table (“SFT”).
Forwarding logic 250 examines at the destination address (“DA”) of a received Ethernet frame. This now becomes the new MAC address, which is then compared with the entries in the SAT. Four different forwarding options are possible. If the destination address is a specific address, known as a “broadcast” address, the frame is destined for all ports on the network. In this case, the Ethernet switch will forward the frame to all ports, except the one on which the frame was received. A broadcast address is six bytes with all ones, or “FF.FF.FF.FF.FF.FF” in hexadecimal notation. If the MAC address is found in the SAT and the corresponding port number is different from the received port, the frame is forwarded to that particular port number only. If the MAC address is found in the SAT and the port number is the same as the received port number, the frame is not forwarded; instead, it is discarded. This is known as “filtering.” The frame is discarded because the transmitting station and the receiving station are connected on the same shared LAN segment on that particular port and the receiver has already tuned into the frame. If the MAC address is not found in the table, the frame is forwarded to all ports. The reason a particular destination address is not present in the SAT table is that the receiving device could be new on the network, or the recipient has been very quiet (has not recently sent a frame). In both cases, the bridge SAT will not have a current entry. Flooding the frame on all ports is the brute way of ensuring that the frame is routed to its intended recipient.
Ethernet switch 200 uses the “age” entry in the SAT to determine whether that MAC address is still in use on the LAN. If the age has exceeded a certain preset value, the entry is removed. This conserves memory space and makes the bridge faster because fewer entries need to be scanned for address matching. Finally, the frame buffer memories 210, 212 will store frames on each port in case there is a backlog of frames to be forwarded.
According to embodiments of the present invention, discovery protocol logic 230 receives, processes, and sends discovery protocol packets to neighboring network devices on the network. Packet redirection logic 260 examines the source and destination addresses of Ethernet packets under control of the configuration and management interface 270 and forwards them to other network devices in a cluster configuration. As known to those skilled in the art, the program code corresponding to discovery protocol logic 230, learning logic 240, forwarding logic 250, packet redirection logic 260, configuration and management interface 270, and other necessary functions may all be stored on a computer-readable medium. Depending on each particular application, computer-readable media suitable for this purpose may include, without limitation, floppy diskettes, hard drives, RAM, ROM, EEPROM, nonvolatile RAM, or flash memory.
An Ethernet LAN switch improves bandwidth by separating collision domains and selectively forwarding traffic to the appropriate segments. FIG. 3 illustrates the topology of a typical Ethernet network 40 in which a LAN switch 42 has been installed. With reference now to FIG. 3, exemplary Ethernet network 40 includes a LAN switch 42. As shown in FIG. 3, LAN switch 42 has five ports: 44, 46, 48, 50, and 52. The first port 44 is connected to LAN segment 54. The second port 46 is connected to LAN segment 56. The third port 48 is connected to LAN segment 58. The fourth port 50 is connected to LAN segment 60. The fifth port 52 is connected to LAN segment 62. The Ethernet network 40 also includes a plurality of servers 64-A-64-C and a plurality of clients 66-A-66-K, each of which is attached to one of the LAN segments 54, 56, 58, 60, or 62. If server 64-A on port 44 needs to transmit to client 66-D on port 46, the LAN switch 42 forwards Ethernet frames from port 44 to port 46, thus sparing ports 48, 50, and 52 from frames destined for client 66-D. If server 64-C needs to send data to client 66-J at the same time that server 64-A sends data to client 66-D, it can do so because the LAN switch can forward frames from port 48 to port 50 at the same time it is forwarding frames from port 44 to port 46. If server 64-A on port 44 needs to send data to client 66-C, which is also connected to port 44, the LAN switch 42 does not need to forward any frames.
Performance improves in LANs in which LAN switches are installed because the LAN switch creates isolated collision domains. Thus, by spreading users over several collision domains, collisions are avoided and performance improves. In addition, many LAN switch installations dedicate certain ports to a single users, giving those users an effective bandwidth of 10 Mbps when using traditional Ethernet.
As a LAN grows, either due to additional users or network devices, additional switches must often be added to the LAN and connected together to provide more ports and new network segments. One way to connect multiple LAN switches together is to cascade them using high-speed ports. However, when cascading LAN switches, the interswitch bandwidth is limited by the number of connections between switches.
Referring now to FIG. 4, two LAN switches 70-A and 70-B are shown, connected in a cascaded configuration. As shown, each of the LAN switches 70-A and 70-B contains eight ports, 72-A-72-H and 74-A-74-H. On each of the LAN switches 70-A and 70-B, four ports 72-A-72-D and 74-A-74-D are connected to computer workstations 76-A-76-D and 76-E-76-H, respectively. The other four ports on each LAN switch (i.e., ports 72-E-72-H on LAN switch 70-A, and ports 74-E-74-H on LAN switch 70-B) are dedicated to interswitch communication. For example, if each of the four interswitch connections is capable of supporting a 100 Mbps. Fast Ethernet channel, the aggregate interswitch communication rate of the switches connected as shown in FIG. 4 is 400 Mbps. However, the total number of ports available for connecting to workstations or other network devices on each LAN switch is diminished due to the dedicated interswitch connections that are necessary to implement the cascaded configuration.
As a LAN grows, network devices are typically added to the LAN and interconnected according to the needs of the particular LAN to which they belong. For example, FIG. 5 illustrates an exemplary group of network devices in a LAN 78, and the interconnections between the network devices in the LAN 78. As shown in FIG. 5, the LAN 78 includes seven network devices: six LAN switches 80-A-80-F and a router 82. Each network device is connected to one or more of the other network devices in the LAN 78. Computer workstations, network printers and other network devices are also connected to the LAN 78, but not shown. It is to be understood that the LAN configuration shown in FIG. 5 is exemplary only, and not in any way limiting.
Regardless of the method used to interconnect them, network devices such as LAN switches need to be configured and managed, because they typically include a number of programmable features that can be changed by a network administrator for optimal performance in a particular network. Without limitation, such features typically include whether each port on the network device is enabled or disabled, the data transmission speed setting on each port, and the duplex setting on each port. Many commercially-available network devices contain embedded HTML Web servers, which allow the network device to be configured and managed remotely via a Web browser.
Traditionally, network device installation includes inserting the device into the network and assigning it an Internet Protocol (“IP”) address, which is a 32-bit number assigned to hosts that want to participate in a TCP/IP Internet. The IP address of a network device is a unique address that specifies the logical location of a host or client on the Internet.
Once a network device has been assigned an IP address, a network administrator can enter the device's IP address or URL into a Web browser such as Netscape Navigator™, available from Netscape Communications Corp. of Mountain View, Calif., or Internet Explorer™, available from Microsoft Corporation of Redmond, Wash., to access the network device and configure it from anywhere in the Internet. However, each network device to be configured must have its own IP address, which must be registered with a domain name service (“DNS”). Assigning an IP address to each and every network device is undesirable, because registering IP addresses with a DNS is both costly and cumbersome.
Accordingly, it would be convenient for a network administrator to be able to assign a single IP address to one network device in a cluster, and then to be able to configure and manage all of the network devices in the cluster using this single IP address. Unfortunately, no current mechanism exists to enable this activity. Thus, it is an object of the present invention to provide a method and apparatus which permits an entire cluster of network devices to share a single IP address. A further goal of the present invention is to enable the clustering of LAN switches or other network devices so that they can be managed through a single network device. Another goal of the present invention is to enable the automatic discovery of switches or other network devices on a LAN that are capable and ready to become part of a cluster.
In the prior art, this goal has been met by using special hardware such as ports, cables, and external backbone matrices. However, according to aspects of the present invention, this goal is achieved without requiring special hardware, and other devices can be found in a network which are capable of being managed through a single network device using only software.